Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1997-01-29
2001-01-09
Hendricks, Keith D. (Department: 1652)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C435S194000, C536S023500
Reexamination Certificate
active
06172210
ABSTRACT:
BACKGROUND OF THE INVENTION
The exposure of phosphatidylserine (PS) and other aminophospholipids (aminoPL) on the surface of activated or injured blood cells and endothelium is thought to play a key role in the initiation and regulation of blood coagulation. De novo surface exposure of aminophospholipids has also been implicated in the activation of both complement and coagulation systems after tissue injury, and in removal of injured or apoptotic cells by the reticuloendothelial system. Although migration of these phospholipids (PL)from inner-to-outer plasma membrane leaflets is known to be triggered by elevated intracellular [Ca
2+
] ([Ca
2+
]
i
) and to be associated with vesicular blebbing of the cell surface, little is known about the cellular constituents that participate in this process.
Role of Cell Surface PS in Coagulation
Several enzyme complexes of the coagulation cascade require assembly on a receptive membrane surface for full expression of catalytic activity (K. G. Mann, et al.,
Annu. Rev. Biochem.
57:915-956, 1988; S. Krishnaswamy, et al.,
J. Biol. Chem.
267:26110-26120, 1992; P. B. Tracy,
Semin. Thromb. Hemost.
14:227-233, 1988). In the case of the tenase (FVIIIaFIXa) and prothrombinase (FVaFXa) complexes, this surface catalytic function of the plasma membrane is not normally expressed by quiescent cells, but is rapidly induced upon cell activation (in platelets) or upon cell injury (in platelets, endothelium and other cells) (E. M. Bevers, et al.,
Blood Rev.
5:146-154, 1991; J. Rosing, et al.,
Blood
65:319-332, 1985; E. M. Bevers, et al.,
Eur. J. Biochem.
122:429-436, 1982; E. M. Bevers, et al.,
Biochim. Biophys. Acta
736:57-66, 1983; T. Wiedmer, et al.,
Blood
68:875-880, 1986). Although specific cell surface protein receptors for FVa and FVIIIa have been postulated, these factors show specific avidity for PS-containing liposomes, and in cell-free systems, this lipid alone can support the catalytic function of the prothrombinase and tenase enzymes (J. Rosing, et al., supra, 1985; M. E. Jones, et al.,
Thromb. Res.
39:711-724, 1985; G. E. Gilbert, et al.,
Biochemistry
3 2:9577-9585, 1993; G. E. Gilbert, et al.,
J. Biol. Chem.
265:815-822, 1990; G. E. Gilbert, et al.,
J. Biol. Chem.
267:15861-15868, 1992). We and others have shown that PS rapidly moves to the surface of plasma membrane upon platelet stimulation, and that this exposure of PS correlates with expression of the platelet's FVa & FVIIIa binding sites and expression of surface catalytic function for tenase and prothrombinase (P. Williamson, et al.,
Biochemistry
31:6355-6360, 1992; F. Basse, et al.,
Biochemistry
32:2337-2344, 1993; C.-P. Chang, et al.,
J. Biol. Chem.
268:7171-7178, 1993; J. Connor, et al.,
Biochim. Biophys. Acta
1025:82-86, 1990; P. Comfurius, et al.,
Biochim. Biophys. Acta.
1026:153-160, 1990). Smeets, et al.,
Biochem. Biophys. Acta Biomembr.
1195:281-286, 1994, Williamson, et al.,
Biochem.
34:10448-10455, 1995; Bratton D. L.,
J. Biol. Chem.
269:22517-22523, 1994). Additional evidence that surface-exposed PS provides the physiological receptor site for these enzyme complexes is provided by (1) the capacity of PS-containing liposomes or phosphoserine to compete binding of FVIIIa to activated platelets (G. E. Gilbert, et al.,
J. Biol. Chem.
266:17261-17268, 1991), (2) the capacity of annexin V and other proteins with affinity for membrane PS to mask the FVa and FVIIIa binding sites expressed by activated platelets (P. Thiagarajan, et al.,
J. Biol. Chem.
265:17420-17423, 1990; P. Thiagarajan, et al.,
J. Biol. Chem.
266:24302-24307, 1991; J. Dachary-Prigent, et al.,
Blood
81:2554-2565, 1993; J. Sun, et al.,
Thromb. Res.
69:289-296, 1993); (3) evidence that platelets congenitally deficient in inducible FVa and FVIIIa receptors are also defective in stimulated exposure of membrane PS (“Scott syndrome”; see below) (J. P. Miletich, et al.,
Blood
54:1015-1022, 1979; J. Rosing, et al.,
Blood
65:1557-1561, 1985; P. J. Sims, et al.,
J. Biol. Chem.
264:17049-17057, 1989; S. S. Ahmad, et al.,
J. Clin. Invest.
84:824-828, 1989; F. Toti, et al.,
Blood
87:1409-1415, 1996). In addition to the catalytic function PS provides to the prothrombinase and tenase complexes, surface exposed aminophospholipids have been shown to promote the activities of the tissue factor-FVIIa and protein S-activated protein C enzyme complexes of the coagulation system, as well as the activity of the alternative pathway C3-convertase (C3bBb enzyme complex) of the complement system (W. Ruf, et al.,
J. Cell. Biol.
266:2158-2166, 1991; F. J. Walker,
J. Biol. Chem.
256:11128-11131, 1981; R. H. Wang, et al.,
J. Clin. Invest.
92:1326-1335, 1993; P. F. Neuenschwander, et al.,
Biochemistry
34:13988-13993, 1995).
In addition to the central role that inducible expression of plasma membrane PS is thought to play in the platelet hemostatic response, the surface exposure of PS and phosphatidylethanolamine (PE) in response to membrane injury has been implicated in a variety of thrombotic and inflammatory disorders. For example, repeatedly sickled SS hemoglobin erythrocytes exhibit increased surface exposure of PS, which promotes prothrombinase assembly and accelerates plasma clotting in vitro, and may contribute to thrombotic complications that can arise in sickle cell disease (P. F. Franck, et al.,
J. Clin. Invest.
75:183-190, 1985; N. Blumenfeld, et al.,
Blood
77:849-854, 1991). Increased PE exposure on sickled RBCs (and other cells) has also been shown to promote complement activation with resulting accumulation of C3b/C3d and C5b-9 on the cell surface, potential factors contributing to the accelerated clearance and increased fragility of these cells (R. H. Wang, et al., supra, 1993). PS exposure secondary to immune injury to the endothelium has also been implicated in the thrombo-embolic complications of hyperacute graft rejection, and PS exposure secondary to C5b-9 accumulation on platelets and red cells has been suggested to contribute to the high risk of venous thrombosis in Paroxysmal Nocturnal Hemoglobinuria (J. L. Platt, et al.,
Immunol. Today
11:450-6; discuss, 1990; A. P. Dalmasso,
Immunopharmacology
24:149-160, 1992; A. P. Dalmasso, et al.,
Am. J. Pathol.
140:1157-1166, 1992; T. Wiedmer, et al.,
Blood
82:1192-1196, 1993, K. K. Hamilton, et al.,
J. Biol. Chem.
265:3803-3814, 1990; S. P. Kennedy, et al.,
Transplantation
57:1494-1501, 1994)). In the “antiphospholipid syndromes,” the interaction of exposed plasma membrane PS and PE with plasma proteins is now generally believed to induce offending antigens (M. D. Smirnov, et al.,
J. Clin. Invest.
95: 309-316, 1995).
Relationship of PS Exposure to Programmed Cell Death
Programmed cell death (apoptosis) is now recognized to be central to the selective elimination of mammalian cells during embryogenesis, tissue re-modeling, and in the clonal selection of immune cells (P. D. Allen, et al.,
Blood Rev.
7:63-73, 1993; J. J. Cohen,
Immunol. Today
14
:
126
-
130
,
1993
). The apoptotic cell undergoes characteristic changes, including elevated [Ca
2+
]
i
, altered phospholipid packing, surface exposure of PS, plasma membrane blebbing and vesiculation, cell shrinkage, chromatin condensation, nucleolar desintegration, and at late stages, DNA degradation by Ca
2+
/Mg
2+
-dependent endonuclease(s), with characteristic fragmentation into 180 bp multimers (“DNA laddering”). The transcriptional events that initiate apoptosis remain unresolved, but evidence implicates certain proto-oncogenes, including c-myc as activators, and other proto-oncogenes, including bcl-2, as suppressors (P. D. Allen, et al., supra, 1993; J. C. Reed,
J. Cell. Biol.
124:1-6, 1994). In thymocytes and B-lymphocytes, an apoptotic transformation can be induced by dexamethasone (activating glucocorticoid receptors) and by cAMP (protein kinase A pathway) (D. J. McConkey, et al.,
J. Immunol.
145:1227-1230, 1990; N. Kaiser, et al.,
Proc. Natl. Acad. Sci. USA
74:638-642, 1977; J.
Sims Peter J.
Wiedmer Therese
Blood Center Research Foundation
Hendricks Keith D.
Quarles & Brady LLP
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